Stabilization method



Sept. 10, 1957 w. 1 vERMlLloN, JR

STABILIZATION METHOD Filed Dec.

United States Patent STABHZATON METHQD Willas L. Vermilion, Jr., Mentor, Ohio, assigner to The Standard Git Company, Cleveland, Ohio, a corporation of Ohio Application December 23, 1953, Serial No. 399,907 1 Claim. (Cl. 19o-11) The present invention relates to a method of stabilizing the condensible products of hydrocarbon reforming processes.

In catalytic hydrocarbon reforming processes, a term used herein to include hydroforming, a process primarily for dehydrogenating the naphthenes or saturated cyclic hydrocarbons in straight-run gasolinas into aromatic compounds, and platforming, a relatively new catalytic reforming process utilizing a platinum catalyst for converting the naphthenes to aromatics, hydrocracking and isomerizing the parafiins, and virtually completely desulfurizing the hydrocarbons, the products leaving the reaction zone, hereinafter referred to as the reformate vapors, comprise mixtures of C3, C4 and higher boiling hydrocarbons, as well as gases such as hydrogen, hydrogen sulde, methane and C2 hydrocarbons, referred to in the art and in the present description as non-condensible gases.

It is the general practice in the art to pass all or part of the reformate vapors through suitable heat exchangers and, after reducing the temperature and pressure thereon and thereby separating the bulk of the non-condensible gases from the condensible hydrocarbons, to subject the latter to stabilization. The stabilization step in elect involves passing the condensed hydrocarbons through one or a series of fractionating towers. One typical stabilization procedure, for example, is that of passing the condensed hydrocarbons under a pressure of say 300 p. s. i. g. into a depropanizer, a tower having a plurality of trays in which the contents are maintained at a considerably higher temperature at the bottom than at the top. The temperatures in the depropanizer are so adjusted that all of the C3 and lower boiling hydrocarbons and other residual gases and an appreciable portion of the C4 hydrocarbons are removed as overhead and the stabilized reformate, consisting of C4 and lower boiling hydrocarbons, is removed at the bottom. The overhead is normally cooled to condense the Ca and C4 hydrocarbons and separate the lower boiling constituents, and the condensed Ca and C4 hydrocarbons are subjected to fractionation in a debutanizer to separate the C3 hydrocarbons from the C4 hydrocarbons and provide a supply of C4 hydrocarbons for redux to the depropanizer.

It has now been found that the stabilization of reformate vapors, particularly those containing a relatively high proportion of non-condensible gases, can be carried out much more electively by interposing between the steps of (a) separating the bulk of the non-condensible gases from the bulk of the condensible hydrocarbons and (b) stabilizing the condensible hydrocarbons, the steps of reducing the pressure on the hydrocarbons condensed in the first step and thereafter increasing the pressure thereon to that at which stabilization is effected. By so reducing the pressure on the condensed hydrocarbons,

Patented Sept. 10, 1957 ICC substantially all of the non-condensible gases that are dissolved in -the condensed hydrocarbons can be removed at an early stage. This early removal of almost all of the non-condensible gases dissolved in the condensed hydrocarbons has a considerable number of advantages. One advantage is that the pressure required to operate the stabilizer is reduced and that consequently the loss of stabilized reformate is reduced to a minimum. Another is that the overhead from the stabilizer is made more readily condensible by recycling condensed Ca hydrocarbons, which in turn makes it possible to substitute a propane reiiux for a butane reflux to the stabilizer and thereby to eliminate the need for a debutanizer.

The advantages and utility of the invention will become further apparent from the following example, in which reference is made to the accompanying drawing:

EXAMPLE Reformate vapors, at 450 p. s. i. g. and 900 F., comprising a mixture from a platformer of C3, C4 and higher boiling hydrocarbons with non-condensible gases such as hydrogen sulfide, hydrogen, methane and C2 hydrocarbons, are passed through line 1 into a primary separator 2 wherein the temperature is reduced to 100 F. Without any substantial change in pressure. The bulk of the noncondensible gases is removed by way of line 4, one portion thereof being recycled to the platformer by way of line 6, and the balance being passed to the platformer absorber by way of line 7. The bulk of the platformate is condensed and passed by way of lines 9 and 10 to a secondary separator 11 in which the pressure is reduced to p. s. i. g. Almost all of the residual non-condensible gases dissolved in the condensed platformate are removed by way of line 12 to a low pressure thermal absorber or the like (not shown) and the condensed platforrnate, now substantially free from dissolved non-condensible gases, is passed by way of line 14, pump 16 (by means of which the pressure is increased to 250 p. s. i. g.), and line 17 to a depropanizer 19.

A stabilized platformate, consisting of C4 and higher boiling hydrocarbons, is removed from the bottom by way of line 20 and Ca and lower boiling hydrocarbons and any residual gases are removed as overhead by way of line 21. The overhead from the depropanizer 19 is subjected to condensation in a condenser 22 and passed by way of line 24 into a receiver 26. The non-condensed gases are recycled by way of line 27 to line 9 and the condensed gases are divided, one portion being reuxed to the depropanizer 19 by way of line 2S and the other portion being passed, by way of line 29, pump 30 (by means of which the pressure is raised to 500 p. s. i. g.) and line 31, into a deethanizer 32.

The bottoms of the deethanizer 32, consisting primarily of C3 hydrocarbons, are removed by Way of line 34, one portion thereof being recycled by way of line 36 to the line 21 to assist in condensing the overhead C3 and lower boiling gases from the depropanizer 19, and the remainder being passed by way of line 37 to storage. The overhead from the deethanizer 32 passes by way of line 39 through a condenser 40 and from thence into a receiver 41 in which the condensed hydrocarbons are reiiuxed to the deethanizer 32 by way of line 42, and the non-condensed lower boiling gases are removed by way of line 44.

A material balance of the operation described is set forth below, the numbers of the column headings corresponding to the reference numerals on the drawing:

Material balance--mol/hour 0.14 0.2 0.1 0.3 0.1 0.2 0.5 884. 0 26. 0 3. 2 29. 2 25.9 3. 3 0. 5 57.1 .9.4 5.1 14.5. 8.4 6.1 4.8 41. 3 34. o 21. 5 55. 5 12. 7 42. s 110 32. 4 Y 85. 6 34. 5 120.1 9. 8 110. 3 657 5.9 37. 2 0.1 37.3 1. 4 35. 9 6. 7 5.6 58.1 0.1 58.2 1.6 55.6 6.7 A2.3 56.1 53.1 0.5 55.5 1.4 37. 7 37. 7 0.3 37.4 6.9 798.4 798.4 1.1 797.3 177.8 177.8 o. 2 177. 6

i 1 Crhydrocarbons plus hydrocarbons having boiling points up to 340 F.

2 Hydrocarbons having 'boiling points-above 340 F.

It will .be noted that of the 26 mols/hour hydrogen dissolved in the platfonnate condensed in .the primary separator 2 and the 3.2 niels/hour dissolved in said platformate by virtue of the recycling of gas from the receiver .26, 25.9 -mols/hour, i. e., approximately 90%, is removed at the secondary separator 11 by way of line 12 leaving only 3.3 mois/hour of hydrogen dissolved in the platformate passed to the depropanizer 19. Furthermore, it will be noted as a direct result of the surprisingly effective removal of hydrogen, that the net amount of C4 hydrocarbons in the overhead 21 from the depropanizer is merely 1.6 mols/hour, i. e., less than 0.8% of the C4 hydrocarbons originally in the platformate vapors. It is also apparent that the yield of stabilized platformate, 1164.7 rnols/hour, is surprisingly high in view of the 1320.5 mols of liquid separated in the primary/separator 2. Y

It is to be understood that various modifications and applications of this method will readily occur to those skilled in the art upon reading this description. All such modifications andapplications are intended to be included within the scope of the appended claims.

I claim:

In Ia method for recovering a stabilized gasoline and a liquetied gas principally comprising the C3 hydrocarbonsfrom the products of .a catalytic hydrocarbon reforming operation, said .products comprising a gaseous mixture, at elevated temperature and pressure, of C1, C2, C3, and higher boiling hydrocarbons with a substantial quantity of hydrogen, the steps which comprise reducing the temperature of said products without substantially reducing the pressure .thereon in a primary separation zone for liquefying Yand separating the bulk of the hydrogen and C; and Cz hydrocarbons as gases from the bulk of the liquid .C3 and higher boiling hydrocarbons and residual dissolved hydrogen and C1 and Cz hydrocarbons, reducing the pressure on the liquefied product from said primary separation zone to a pressure below a depropanization pressure in a secondary separation zone whereby substantially vall of the residual hydrogen is removed as a gas from said liquefied product without an appreciable loss of hydrocarbons boiling above the C3 hydrocarbons, raising the Vpressure von the liquid product from said secondary separation -zone lto said depropanizing pressure, passing-said liquid product at saiddepropanizing pressure to a tir-st fractionation zone and adjusting the temperatures therein whereby substantially all of the C1, C2 andy Ca hydrocarbons ,are removed from said liquid product and substantially all of the .C4 hydrocarbons are retained in said liquid product, recovering said liquid product from the bottom of said .first fractionation zone, condensing the overhead product from said iirst fractionation Yzone, recycling a portion of said condensed overhead product to said 'tirst fractionatigng zone,raising the pressure on the remainder of said condensed overhead product to Ha deethanization ,pressure and, passing said remainder Vat said deethanization pressure to a second fractionation zone and adjusting .the temperatures therein, recycling an lappreciable portion of lthe bottom product from said lsecond fractionation zone which comprises a major quantity of C3 hydrocarbons, admixing said portion of the bottom product of said second fractionation zone with the overhead` product of said irst fractionation zone prior to said condensation step, and recovering the'remainder of the bottom product from said second fractionation zone.

References Cited inthe tile of this patent UNITED STATES PATENTS 2,073,073 Roberts .Man 9, 1937 2,666,019 et a1. Jan. 121, 195,4 V2,719,816 Rich Oct. 4, 1955 

